The present invention relates to an improved ink jet ink, and in particular a pigmented ink jet ink. The present invention also relates to a process for the preparation of such pigmented ink jet inks.
Ink jet recording systems are advantageous in that they make very little noise when recording, can be readily matched to color recording, and can also obtain the recorded image with high resolution at a high speed. Inks which are suitable for use in an ink jet printing system should display a consistent drop breakup length, drop velocity and, for synchronous ink jet printing, drop charge under set operating conditions. Conventional ink jet inks are complex multicomponent systems based on water soluble dye(s), further containing polymers, solubilizing agents, chelating agent and biocides.
Several drawbacks plague the use of dye-containing, water-based inks. Dyes suffer a limited color selection and gamut when compared to pigments. This results in limited color reproduction. Furthermore, dyes are not as lightfast and waterfast as pigments. The water solubility of the dyes limits their use in that the images cannot get wet or be used outdoors. Dyes also tend to wick and bleed into uncoated and rough papers. The degree of spreading depends upon the paper used. Thus, the range of paper which can be used with dye-based inks is limited. In addition there is a loss in image resolution due to feathering and intercolor bleeding of image characters on the paper.
Because of the limitations of the water-soluble dye approach, researchers have worked with pigment-based inks. Although pigment-based inks are more lightfast and waterfast and can be used with a wide range of papers, it is still very difficult to obtain particles small enough which do not settle and clog the orifice of the printing system. The orifice must remain open for a wide range of operating conditions, e.g., temperature and humidity. Problems of feathering, migration and image loss can also occur with pigment inks.
Conventional processes for preparing pigment-based ink jet inks include blending ink jet materials together and then mixing and grinding with a known dispersing device such as a ball mill, homomixer, sand mill or roll mill. U.S. Pat. No. 4,597,794 describes a process wherein the pigmented ink jet ink is prepared by dispersing fine particles of pigments in an aqueous dispersion medium containing a polymer having both a hydrophilic and hydrophobic construction portion. The components were prepared using the aforementioned standard processes.
U.S. Pat. No. 5,026,427 relates to a process for making pigmented ink jet inks. The process involves mixing at least one pigment and at least one pigment dispersant in a medium comprised of water or water in a water soluble organic solvent. The pigmented ink mixture is then deflocculated by passing it through a microfluidizer.
U.S. Pat. No. 5,160,370 relates to a pigmented ink which involves a pigment, a water soluble resin, a water soluble organic solvent and water. The water soluble resin is added in an amount such that the amount of resin not absorbed on the pigment is about two percent or less. Furthermore, the water soluble organic solvent comprises at least one polyhydric alcohol and an aliphatic monohydric alcohol, such as ethanol.
Due to the complex nature of the composition of an ink, the composition and the method used to produce the ink can be quite sensitive. There is a need in the industry to improve the inks used, as well as the methods used to manufacture the inks. Solutions are directed to improving the migration and featherability of the inks when creating the image, as well as the plugging of the nozzle in the ink jet printer. Among the solutions proposed have been the following.
In European Patent Application 057119082, natural polysaccharides have been employed together with surfactants and binder. The use of the sugar, however, can create sugar water soluble substances on the surface of the image, which can destabilize and produce a white bloom on a colored background.
In U.S. Pat. No. 5,173,112, the question of nozzle plugging is addressed. Alkyl amides and cyclic amides are used as special co-solvents. U.S. Pat. Nos. 5,205,861 and 5,169,438 also address the nozzle plugging problem and employ cyclo aliphatic diol pluggage inhibitors.
U.S. Pat. No. 5,221,334 discloses nonionic and ionic mechanisms of pigmented ink stabilization. The patent describes the use of AB or BAB block copolymers with the A segment being a hydrophobic copolymer and the B segment being a hydrophilic polymer or salt. The block copolymer is neutralized by huge amounts of sodium hydroxide, and the materials are milled.
Despite the foregoing attempts to solve many of the problems which exist, there is nevertheless a need to improve the pigmented inks used in ink jet printers, both from the standpoint of the image printed and the printability of the inks.
Accordingly, one object of the present invention is to provide a novel ink jet ink composition.
Another object of the present invention is to provide an ink jet ink composition which demonstrates improved printability.
Yet another object of the present invention is to provide an ink jet ink which prints an image of high density and with high resolution, and is devoid of the problems of feathering and migration.
Another object of the present invention is to provide a process for preparing such a novel pigmented ink jet ink.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.